To provide an automatic bookmaker which can automatically and newly position its book marking body when pages are turned either forward or backward and also can reduce its projecting portion from the book by providing two or more arms therewith.

The automatic bookmaker includes: bases 4 fixed to the front cover and the back cover of a book; shoulders 3 provided at upper ends of the front cover side and the back cover side of the base 4; flexible arms 2 which extend from the respective shoulders 3 toward the opening and closing axes of the book; and a single book marking body 1 supported by free ends of the respective arms 2. The automatic bookmaker is characterized in that, when the book is opened, the upper arms 2 move the book marking body 1 toward directions of front and back sides of the book and move and keep the book marking body 1 between the opened pages while inserting the end of the book marking body 1 between the last opened pages when the book is closed.